Cover tape

ABSTRACT

The present invention relates to a cover tape and to an electronic component package that uses the cover tape, the cover tape including at least a substrate layer, a heat seal layer, and an antistatic layer, the antistatic layer containing (A) an ionic liquid including a cyclic quaternary nitrogen-containing cation, (B) a quaternary ammonium salt, and (C) a polyalkylene glycol being formed on a surface toward the heat seal layer, and an anion constituting the (A) ionic liquid including a cyclic quaternary nitrogen-containing cation and the (B) quaternary ammonium salt being one or more anions selected from the group consisting of carboxylic acids, sulfuric acid esters, phosphoric acid esters, sulfonic acids, and phosphoric acids.

TECHNICAL FIELD

The present invention relates to a cover tape used as a lid material forcarrier tape used to transport chip-type electronic components untilthey are mounted on substrates.

BACKGROUND ART

When transporting chip-type electronic components such as ICs, carriertapes are generally used. In other words, the aforementioned chip-typeelectronic components are inserted into dimples for housing electroniccomponents formed at standard intervals on the carrier tape, the topsurface of the carrier tape is heat sealed with cover tape having aneasily peelable adhesive layer on a substrate to seal the electroniccomponents, then wound into a reel for transport. While theaforementioned cover tape must be transparent enough to enableinspection of the electronic components and to enable it to be smoothlypeeled from the carrier tape with ease, if the electronic components arealso components that easily undergo insulation breakdown due to staticelectricity from ICs or the like, one or both surfaces of the cover tapemay be treated with an antistatic treatment in order to preventadherence of dust, protect the contents from static electricity, andprevent problems such as the electronic components sticking to the covertape and flying out when the cover tape is peeled from the carrier tape.

The antistatic treatment may be performed using a method such asblending an antistatic agent into the resin forming the surface to bestatic-proofed, or by thinly coating the surface with an antistaticagent. Examples having an antistatic agent coated onto the surface of anadhesive layer (or heat seal layer) are disclosed in Patent Documents 1and 2.

With these methods, antistatic agent must be coated in bulk to obtainsufficient antistatic effects, and when placed in a high-temperaturehigh-humidity environment while heat sealed to carrier tape, theyattract oxygen and moisture from the air, causing reductions in theadhesive force of the cover tape as a result of which vibrations duringtransport and mounting can cause the cover tape to peel, and theelectronic components may spill out.

Additionally, methods of static-proofing cover tape by coating thesurface of the adhesive layer (heat seal layer or sealant layer etc.)with a coating containing conductive microparticles have been proposed(e.g., Patent Documents 3, 4 and 5). However, with these methods, it isnot easy to evenly disperse microparticles in the resin componentsforming the coating material, and this not only complicates themanufacturing process and reduces productivity, but also causesdispersion defects. Additionally, in the latter method wherein anantistatic agent is kneaded in, sufficient surface resistance cannot beobtained, and mixing metal microparticles may cause the transparency todrop, making it difficult to achieve enough transparency to be able toobserve printing or the shapes of contents through the cover tape.

On the other hand, in recent years, a coating-type antistatic agentusing an ionic liquid has been proposed for static-proofing films orsheets in general (e.g., Patent Document 6). However, there do not seemto be any documents that disclose coating the surface of the heat seallayer of cover tape, or its effect on peel strength.

-   Patent Document 1: JP H7-172463 A-   Patent Document 2: JP 2005-225548 A-   Patent Document 3: JP H11-115088 A-   Patent Document 4: JP H7-251860 A-   Patent Document 5: JP 2003-266016 A-   Patent Document 6: JP 2010-121093 A

SUMMARY OF THE INVENTION

The present invention addresses the problem of offering a cover tapeused in a lid material for a container such as carrier tape for housingcomponents and a chip-type electronic component package using said covertape, wherein the cover tape has good transparency and sufficientantistatic properties, and when housing and storing components, iscapable of sufficiently suppressing decreases in peel strength withrespect to carrier tape even when used in high-temperature high-humidityenvironments, and does not cause problems such as corrosion of thecontents.

As a result of diligent consideration of the aforementioned problem, thepresent inventors discovered that decreases in peel strength can besufficiently suppressed even in high-temperature high-humidityenvironments, by forming an antistatic layer containing a specificantistatic agent comprising an ionic liquid on a surface on a heat seallayer side, thereby achieving the present invention.

That is, in one aspect, the present invention relates to a cover tapecomprising at least a substrate layer, a heat seal layer and anantistatic layer, wherein the antistatic layer comprises (A) an ionicliquid containing a cyclic quaternary nitrogen-containing cation, (B) aquaternary ammonium salt and (C) a polyalkylene glycol, and is formed onthe surface on the heat seal layer side. In one embodiment, anions in(A) the ionic liquid containing a cyclic quaternary nitrogen-containingcation and (B) the quaternary ammonium salt are preferably of one ormore types chosen from the group consisting of carboxylic acids,sulfuric acid esters, phosphoric acid esters, sulfonic acids andphosphoric acids. In another embodiment, the ratios of the content ofthe components of the antistatic layer are preferably 10 to 80 mass % ofcomponent (A), 5 to 70 mass % of component (B) and 5 to 50 mass % ofcomponent (C).

In one embodiment, (A) the ionic liquid containing a cyclic quaternarynitrogen-containing cation is preferably an imidazolium salt. In anotherembodiment, the cations in (B) the quaternary ammonium salt shouldpreferably have one alkyl group or alkenyl group having 10 to 20 carbonatoms. In a further embodiment, (C) the polyalkylene glycol shouldpreferably be a polyethylene glycol having a mass-average molecularweight (Mw) of 200 to 600. In yet another embodiment, the thickness ofthe antistatic layer on the surface on the heat seal side is 0.01 to 0.2μm.

Furthermore, in another aspect, the present invention relates to anelectronic component package using one of the aforementioned covertapes.

The cover tape of the present invention is a cover tape havingtransparency that can be easily peeled from carrier tape, has sufficientantistatic effects and anti-rust effects, and is capable of suppressingdecreases in adhesive force of the cover tape and notably suppressingspillage of electronic components due to vibrations during transport ormounting even when housing and storing electronic components inhigh-temperature high-humidity environments.

MODES FOR CARRYING OUT THE INVENTION

The cover tape of the present invention comprises at least a substratelayer, a heat seal layer and an antistatic layer. In other words, it mayhave a three-layered structure of a substrate layer, a heat seal layerand an antistatic layer, or it may have a multilayered structure withone or more intermediate layers between these layers. In the case of amultilayered structure, an antistatic layer containing an antistaticagent comprising (A) an ionic liquid containing a cyclic quaternarynitrogen-containing cation, (B) a quaternary ammonium salt and (C) apolyalkylene glycol is formed on the surface on the heat seal layerside.

Herebelow, each layer will be described in detail.

<Substrate Layer>

The substrate layer comprises a thermoplastic resin, and is preferably,for example, a film, particularly a biaxially stretched film, producedfrom a thermoplastic resin which may be a polyester such as polyethyleneterephthalate or polyethylene napththalate, a polyolefin such aspolypropylene, a polyamide such as nylon, or a polycarbonate. It ispreferably a biaxially stretched polyethylene terephthalate film, and inany case, a commercially available film may be used. While the thicknessof the substrate layer is not particularly limited, one with a thicknessof 5 to 50 μm should generally be used.

The side of the substrate that is to contact the heat seal layer orintermediate layer may be surface-treated by sandblasting, coronadischarge, or plasma treatment to enhance the adhesive strength with theheat seal layer or intermediate layer and stabilize. Additionally, anantistatic agent can be kneaded into the substrate layer, or anantistatic product coated with an antistatic agent may be used on thesurface on the side that is to form the outer surface of the cover tape.Additionally, an anchor coating agent may be provided on the surface ofthe substrate layer for the purpose of raising the adhesive force whenlaminating an intermediate layer or a heat seal layer on the substratelayer.

<Intermediate Layer>

An intermediate layer may be provided between the substrate layer andthe heat seal layer. The intermediate layer comprises a thermoplasticresin, and may be a single layer or multiple layers. By providing anintermediate layer, the cover tape may be provided with cushioning, andthe adhesive force between the substrate layer and the heat seal layermay be strengthened. While the thermoplastic resin used in theintermediate layer is not particularly limited, it may be chosen as oneor a mixture of two or more publicly known resins such as, for example,polyolefin resins including low-density polyethylene resins (LDPE) andvarious linear low-density polyethylene resins (LLDPE) polymerized byZiegler catalysts or metallocene catalysts.

<Heat Seal Layer>

The heat seal layer is not particularly limited as long as it contains athermoplastic resin that has heat-sealability with respect to carriertape and exhibits an easy-peel property enabling it to be easily peeledat the time of use. For example, an ionomer resin, an acid-modifiedpolyolefin resin, an ethylene-(meth)acrylic acid copolymer, anethylene-(meth)acrylic acid ester copolymer, a polyester resin, apolyamide resin, a vinyl resin, an acrylic resin such as an acrylic or amethacrylic, an acrylic acid ester resin, a maleic acid resin, a butyralresin, an alkyd resin, a polyethylene oxide resin, a polyurethane resinand a silicone resin. Preferably, a resin mixture obtained by mixing oneor more resins chosen from among ethylenic polymers such as variouspolyethylene resins, ethylene-vinyl acetate copolymers, ethylene-ethylacrylate copolymers and ethylene-butene-1 random copolymers with one ormore styrenic polymers such as styrene-butadiene copolymers,polystyrenes and impact-resistant polystyrenes in order to adjust thepeel strength when heat-sealing to carrier tape can be used. Morepreferable is a resin mixture of an ethylene-butene-1 random copolymer,a styrene-butadiene copolymer and an impact-resistant polystyrene forhaving a continuously stable peel strength.

Furthermore, the use of a mixture blended at a ratio of 15 to 60 mass %of ethylene-butene-1 random copolymer, 30 to 80 mass % ofstyrene-butadiene copolymer and 3 to 15 mass % of impact-resistantpolystyrene in 100 mass % of the entire resin in the heat seal layer ofthis resin mixture is more preferable for stability of the peel strengthafter being in a high-temperature high-humidity environment.

<Antistatic Layer>

The antistatic layer comprises an antistatic agent comprising (A) anionic liquid containing a cyclic quaternary cation, (B) a quaternaryammonium salt and (C) a polyalkylene glycol, and is formed on thesurface of the heat seal layer. The proportional content of thecomponents of the antistatic layer is 10 to 80 mass %, preferably 30 to80 mass % of component (A), 5 to 70 mass %, preferably 10 to 40 mass %of component (B) and 5 to 50 mass %, preferably 10 to 30 mass % ofcomponent (C).

Examples of the cation in the ionic liquid (hereinafter referred tosimply as “(A) ionic liquid”) containing (A) a cyclic quaternarynitrogen-containing cation include imidazolium cations, pyridiniumcations, pyrrolidinium cations, pyrazolium cations and triazoliumcations, among which imidazolium cations, pyridinium cations andpyrrolidinium cations are preferred, and imidazolium cations are morepreferred for being capable of preparing numerous diverse types of ionicliquids of low melting point.

Examples of imidazolium cations include 1,3-dimethylimidazolium,1-butyl-2,3-dimethylimidazolium, 1-butyl-3-methylimidazolium,1-ethyl-2,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium,1-hexyl-3-methylimidazolium and 1-hexyl-3-propylimidazolium, among which1-ethyl-3-methylimidazolium cations are particularly preferable forbeing available in various salts.

Examples of the anions in the (A) ionic liquid include organic acids andsuperstrong acids such as carboxylic acid, sulfuric acid esters,phosphoric acid esters and sulfonic acid, and inorganic acids such asphosphoric acids, hydrogen halides and perhalic acids, among whichsulfuric acid esters are preferable and ethyl sulfate anions are morepreferable for their antistatic properties and prevention of rust on theelectronic components housed in the carrier tape.

The (A) ionic liquid in the present invention may be an ionic liquidcomprising the aforementioned cations and anions. Specific examplesinclude 1,3-dimethylimidazolium ethyl sulfate,1-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-3-methylimidazoliumacetate, 1-butyl-3-dimethylimidazolium phosphate and1,3-dimethylimidazolium hydrogensulfate.

The (B) quaternary ammonium salt is preferably a compound of thefollowing Formula 1:

In the formula, R1 denotes an alkyl group having 10 to 20 carbon atomsor an alkenyl group having 10 to 20 carbon atoms, R2, R3 and R4 denotealkyl groups having 1 to 3 carbon atoms, and X⁻ denotes an anion. Theanion X⁻ may be the same type of anion as in the (A) ionic liquid, andis preferably a sulfuric acid ester, more preferably an ethyl sulfateanion.

Specific examples of the (B) quaternary ammonium salt include trimethyllauryl ammonium methyl sulfate, ethyl dimethyl stearyl ammonium ethylsulfate, ethyl dimethyl oleyl ammonium ethyl sulfate, ethyl dimethyllauryl ammonium ethyl sulfate, ethyl dimethyl stearyl ammoniummeta-sulfonium and ethyl dimethyl lauryl ammonium methanesulfonium.

The antistatic layer used in the present invention contains a (C)polyalkylene glycol as described above. Examples include polyethyleneglycol, polypropylene glycol, polybutylene glycol, polyalkylene oxidessuch as ethylene oxide-propylene oxide copolymers, polyether estershaving ester bonds with polyoxyalkylene structures, polyether amideshaving amide bonds with polyoxyalkylene structures, and polyether esteramides having amide bonds and ester bonds with polyoxyalkylenestructures, among which polyethylene glycol is preferable in view of theavailability and closeness of contact with the heat seal layer surfaceof the coating film. When using polyethylene glycol, the mass averagemolecular weight (Mw) should preferably be in the range of 200 to 600,300 to 500, or about 400 in view of the ease of formation of a coatingfilm and dispersibility of ionic liquid in the film.

As described above, an antistatic layer containing an antistatic agentcomprising the aforementioned components (A), (B) and (C) is formed onthe surface on the heat seal layer side of the cover tape of the presentinvention.

As for the proportional content of each component (A), (B) and (C) inthe antistatic layer, component (A) should preferably be present at 10to 80 mass % with respect to the entire composition. At less than 10mass %, there is a risk of it becoming difficult to obtain a surfaceresistivity providing an adequate antistatic effect, and at more than 80mass %, the viscosity may increase and cause stickiness on the surface.Additionally, component (B) is preferably present at 5 to 70 mass %. Atless than 5 mass %, it may become difficult to obtain sufficientantistatic properties, and at more than 70 mass %, the adhesive force ofthe cover tape may drop in high-temperature high-humidity environments.On the other hand, component (C) should preferably be present at 5 to 50mass %. At less than 5 mass %, it may become difficult to form a uniformfilm for the antistatic layer, and at more than 50 mass %, it may becomedifficult to obtain sufficient peel strength when heat-sealing tocarrier tape.

As is clear from the above, by forming an antistatic layer comprisingthree components (A), (B) and (C), the present invention provides acover tape having good transparency and sufficient antistaticproperties, capable of sufficiently suppressing the peel strength withthe carrier tape when housing and storing components, even for use inhigh-temperature high-humidity environments, without causing anyproblems such as corrosion of the contents.

An antistatic layer is formed by diluting the above antistatic agentwith water or an appropriate organic solvent and coating by a commonmethod. The thickness of the antistatic layer after drying shouldpreferably be 0.01 to 0.2 μm. At less than 0.01 μm, sufficientantistatic properties may not be able to be obtained, and at more than0.2 μm, the heat sealability is reduced, such as with reduced peelstrength. Additionally, a surface resistivity of 1×10¹² Ω/sq or less hasbeen considered to be preferable for obtaining antistatic properties,but 1×10¹² Ω/sq or less is sometimes inadequate due to theminiaturization and higher integration of electronic components inrecent years, so the cover tape requires an antistatic performance of1×10¹¹ Ω/sq or less. Additionally, a low surface resistivity will neverbe a problem in terms of the antistatic properties, but it is notrealistic to expect to achieve values of less than 1×10⁷ Ω/sq byaddition of an antistatic agent.

<Cover Tape>

The cover tape of the present invention has a substrate layer and a heatseal layer as mentioned above. As the method for producing the covertape, it can be formed by a common method such as forming a heat seallayer as a single film by means of T-die extrusion or inflation, andlaminating onto a substrate layer by dry lamination, or extrusionlamination via a low-density polyethylene or the like melt-extruded ontoa substrate layer film. Additionally, when providing an intermediatelayer between the substrate layer and the heat seal layer as mentionedabove, a multimanifold or a feed block can be used to form a laminatedfilm formed by laminating the intermediate layer and the heat seallayer, and laminating this laminated film with the substrate layer bydry lamination or sand lamination with the surface on the intermediatelayer side as the lamination surface, to produce the cover tape of thepresent invention.

The cover tape of the present invention is used as a cover tape fortransporting electronic components to cover the top surfaces of dimpleportions in carrier tapes having electronic component-housing dimpleportions for housing electronic components formed in a central portionin the width direction at predetermined intervals in the longitudinaldirection.

<Carrier Tape>

Carrier tape is a ribbon-shaped article of width 8 mm to 100 mm havingdimples for housing electronic components. When heat sealing a covertape as a lid material, the material of the carrier tape is notparticularly limited, and one that is commercially available may beused. For example, polystyrene, polyester, polycarbonate or polyvinylchloride can be used. Additionally, the carrier tape may be madeconductive by kneading carbon black or carbon nanotubes into the resin,have cationic, anionic or non-ionic surfactant-type antistatic agents ordurable antistatic agents such as polyether ester amides kneadedtherein, or have the surface coated with a surfactant-type antistaticagent or a coating solution having a conductor such as polypyrrole orpolythiophene dispersed in an organic binder such as acryl to provide anantistatic property.

<Electronic Component Package>

A package for housing electronic components or the like is obtained, forexample, by housing electronic components or the like in dimples in thecarrier tape for housing electronic components, then continuouslyheat-sealing both edge portions in the longitudinal direction of thecover tape using a heated iron or the like with the cover tape as a lidmaterial for packaging, and then winding the tape onto a reel.Electronic components are packaged in this form for storage andtransport. The package of the present invention may be used to house andtransport various electronic components such as connectors, ICs, diode,transistors, capacitors, resistors and LEDs, and are especially capableof greatly reducing problems when mounting electronic components in thecase of electronic components such as LEDs, transistors and diodes ofthickness 1 mm or less. The package housing electronic components or thelike is advanced using holes called sprocket holes for advancing thecarrier tape provided at edge portions in the longitudinal direction ofthe carrier tape while successively peeling away the cover tape, and theelectronic components are withdrawn by a component mounting device whileobserving the presence, orientation and position of the electroniccomponents to mount them onto a substrate.

<Other Examples of Use>

As other examples of use of the cover tape of the present invention,there are transports comprising polygonal punched carrier tape havingpolygonal punched holes for housing components, bottom cover tape forcovering the bottom surfaces of polygonal holes in polygonal punchedcarrier tape, and top cover tape for covering the top surfaces ofpolygonal holes in polygonal punched carrier tape. In such transports,the cover tape for transporting electronic components of the presentinvention can be used as a top cover tape.

The cover tape for transporting electronic components of the presentinvention can be favorably used in the form of uses mentioned above totransport a wide range of chip-type electronic components includingresistors such as chip-mounted resistors and capacitors such aslaminated ceramic capacitors.

EXAMPLES

The present invention shall be explained in detail with reference toexamples.

Example 1

A resin mixture comprising 40 parts by mass of a styrene-butadiene blockcopolymer having a styrene content of 80 mass % and a butadiene contentof 20 mass % (Denki Kagaku Kogyo, product name Clearen), 25 parts bymass of a styrene-butadiene block copolymer with a styrene content of 40mass % and a butadiene content of 60 mass % (JSR, product name TRResin), 25 parts by mass of an ethylenic polymer (Mitsui Chemical,product name Tafmer-A) and 10 parts by mass of a high-impact polystyrene(Toyo Styrene H870) was prepared, kneaded at 210° C. using a uniaxialextruder of diameter 40 mm and extruded by a T-die process to produce afilm of thickness 30 μm for use in a heat seal layer.

This film and a biaxially stretched polyethylene terephthalate film wereextrusion sand laminated with a melted low-density polyethylene toproduce a laminated film. A liquid (0.5 mass % solution) obtained bydiluting an antistatic agent comprising 30 mass % of an imidazolium salt(component A) (1-ethyl-3-methylimidazolium ethyl sulfate, Tokyo ChemicalIndustry), 40 mass % of a quaternary ammonium salt (component B) (ethyldimethyl laurylammonium ethylsulfate, NOF Elegan 264 wax) and 30 mass %of a polyethylene glycol (component C) (Mw=400) by 200 times in purifiedwater was applied as an antistatic agent to both surfaces of thelaminated film to a dry thickness of about 0.1 μm, then dried to obtaina cover tape.

Example 2

A cover tape was produced in the same way as Example 1, except that anantistatic agent comprising 80 mass % of an imidazolium salt(1-ethyl-3-methylimidazolium ethyl sulfate, Tokyo Chemical Industry), 10mass % of a quaternary ammonium salt (ethyl dimethyl laurylammoniumethylsulfate, NOF Elegan 264 wax) and 10 mass % of a polyethylene glycol(Mw=400) was used.

Example 3

A cover tape was produced in the same way as Example 1, except that anantistatic agent comprising 30 mass % of an imidazolium salt(1-ethyl-3-methylimidazolium ethyl sulfate, Tokyo Chemical Industry), 40mass % of a quaternary ammonium salt (ethyl dimethyl oleylammoniumethylsulfate) and 30 mass % of a polyethylene glycol (Mw=400) was used.

Example 4

A cover tape was produced in the same way as Example 1, except that anantistatic agent comprising 30 mass % of an imidazolium salt(1-ethyl-3-methylimidazolium ethyl sulfate, Tokyo Chemical Industry), 40mass % of a quaternary ammonium salt (ethyl dimethyl laurylammoniumethylsulfate, NOF Elegan 264 wax) and 30 mass % of a polyethylene glycol(Mw=400) was used.

Comparative Example 1

A cover tape was produced in the same way as Example 1, except that anantistatic agent comprising 70 mass % of a quaternary ammonium salt(ethyl dimethyl laurylammonium ethylsulfate, NOF Elegan 264 wax) and 30mass % of a polyethylene glycol (Mw=400) was used.

Comparative Example 2

A cover tape was produced in the same way as Example 1, except that anantistatic agent comprising 70 mass % of an imidazolium salt(1-ethyl-3-methylimidazolium ethyl sulfate, Tokyo Chemical Industry) and30 mass % of a polyethylene glycol (Mw=400) was used.

Comparative Example 3

A cover tape was produced in the same way as Example 1, except that anantistatic agent comprising 60 mass % of an imidazolium salt(1-ethyl-3-methylimidazolium ethyl sulfate, Tokyo Chemical Industry) and40 mass % of a quaternary ammonium salt (ethyl dimethyl laurylammoniumethylsulfate, NOF Elegan 264 wax) was used.

Comparative Example 4

A cover tape was produced in the same way as Example 1, except that ananionic antistatic agent (Upon LS-250, Lion) was used as the antistaticagent.

Comparative Example 5

A cover tape was produced in the same way as Example 1, except that azwitterionic antistatic agent (Nissananon BF, NOF) was used as theantistatic agent.

Comparative Example 6

A cover tape was produced in the same way as Example 1, except that ametal oxide-containing acrylic resin (Neocon Coat 565DR-2,Dainichiseika) was coated as the antistatic agent on only the heat seallayer side of the same laminated film as Example 1 to a thickness afterdrying of about 0.1 μm.

Comparative Example 7

A cover tape was made in the same way as Example 1 except that only1-ethyl-3-methylimidazolium chloride (Tokyo Chemical Industry) was usedas the antistatic agent. This cover tape had stickiness on theantistatic layer formed on the surface of the heat seal layer and hadproblems in practical application such as adhesion to contents.

(Evaluation Method)

Cover tapes produced in the above-described examples and comparativeexamples were used to make the following evaluations and the results ofthe evaluations are shown together in Table 1.

(1) Surface Resistivity Measurement

A Mitsubishi Chemical Hiresta UPMCP-HT450 was used to measure thesurface resistivity on the heat seal layer side surface and substratelayer side of the cover tape using the method of JIS K6911 in anenvironment of 23° C. and relative humidity 50%, applied voltage 500 Vand measurement time 60 seconds. While a surface resistivity of 1×10¹²Ω/sq or less has conventionally been considered preferable, theminiaturization and higher integration of electronic components inrecent years has made a surface resistivity of 1×10¹¹ Ω/sq or lessnecessary.

(2) Peel Strength

A carrier tape was produced by heat sealing a cover tape prepared asdescribed above to a carrier tape of width 24 mm formed by a Denka ECsheet (thickness 0.4 mm) using a heat sealer under conditions of ironwidth 0.5 mm×2, pressure 0.34 MPa, time 0.5 seconds and two sealings,and the peel strength was measured at a speed of 300 mm/minute. Thosewith a peel strength of less than 0.4 N even when sealed at a sealtemperature of 160° C. had insufficient peel strength for practical useand sometimes became peeled during transport.

(3) Peel Strength Stability in High-Temperature High-HumidityEnvironment

A carrier tape was produced by heat sealing in the same way as insection (2) above. The peel strength of the taped product was measuredafter seven days of storage at high-temperature high-humidity (60° C.,relative humidity 90%), then letting stand for 24 hours at a constanttemperature and constant humidity (23° C., relative humidity 50%). Thosewith a peel strength of less than 0.4 N did not have sufficient peelstrength for practical use, and the housed components sometimes spilledout.

(4) Metal Corrosion

In a progressive environment (60° C., relative humidity 90%), a smallpiece of kovar was placed on the heat seal layer surface of a covertape, and the appearance of the surface of contact with the cover tapewas observed every 24 hours. Observations were performed with a stereomicroscope at 20-times magnification, with the occurrence ofreddish-brown discolorations compared to the surface not contacting thecover tape being observed, and the time elapsed until the occurrencebeing measured. The observations were performed up to 396 hours. It hasbeen confirmed that if no discolorations are observed for more than 336hours in the progressive environment, similar discolorations will not beobserved for one year when actually put on the market.

The evaluation results for the examples and comparative examples areshown together in Table 1.

Comp Comp Comp Comp Comp Comp Comp (Antistatic Layer Composition) (mass%) Ex 1 Ex 2 Ex 3 Ex 4 Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 Ex 6 Ex 7 Component A1-ethyl-3-methyl 30 80 30 30 70 60 imidazolium ethyl sulfate1-ethyl-3-methyl 100 imidazolium chloride Component B Ethyl dimethyllauryl 40 10 40 70 40 ammonium ethyl sulfate Ethyl dimethyl oleyl 40ammonium ethyl sulfate Component C Polyethylene glycol 30 10 30 30 30(Mw: 400) Polyethylene glycol 30 (Mw: 1000) Anionic Antistatic Agent 100Zwitterionic Antistatic Agent 100 Metal Oxide (Acrylic Binder) 100(Properties) Surface Substrate Layer Side 1 × 10⁹ 4 × 10⁹ 3 × 10⁹ 5 ×10⁹ 2 × 10⁹ 2 × 10¹¹ 1 × 10¹⁰ 5 × 10⁹ 7 × 10¹⁰ 1 × 10⁹ Resistivity(Ω/sq) (Ω/sq) Heat Seal Layer Side 1 × 10⁹ 4 × 10⁹ 3 × 10⁹ 5 × 10⁹ 2 ×10⁹ 5 × 10¹¹ 2 × 10¹⁰ 5 × 10⁹ 8 × 10¹⁰ 8 × 10⁹ 1 × 10⁹ (Ω/sq) PeelStrength Standard (N) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.1 0.5 0.5 0.5 HiTemp Hi Humidity (N) 0.5 0.5 0.5 0.4 0 0.5 0 0 0.5 0.5 0.5 Metal TimeUntil Corrosion (h) none none none none none none none none 120 none 72Corrosion

INDUSTRIAL APPLICABILITY

The cover tape of the present invention is a cover tape havingtransparency that can be easily peeled from carrier tape, having goodantistatic effects and being capable of notably suppressing corrosion ofcontents having metal portions such as ICs in high-temperaturehigh-humidity environments, and therefore can be used not only as acover tape for electronic component transporters for transporting andstoring electronic components such as ICs having metal portions, butalso for the transport of a wide range of chip-type electroniccomponents including resistors such as chip-mounted resistors andcapacitors such as laminated ceramic capacitors.

1. A cover tape comprising at least a substrate layer, a heat seal layerand an antistatic layer, wherein the antistatic layer comprises (A) anionic liquid containing a cyclic quaternary nitrogen-containing cation,(B) a quaternary ammonium salt and (C) a polyalkylene glycol, and isformed on the surface on the heat seal layer side.
 2. The cover tapeaccording to claim 1, wherein anions in (A) the ionic liquid containinga cyclic quaternary nitrogen-containing cation and (B) the quaternaryammonium salt are of one or more types chosen from the group consistingof carboxylic acids, sulfuric acid esters, phosphoric acid esters,sulfonic acids and phosphoric acids.
 3. The cover tape according toclaim 1, wherein the antistatic layer contains the respective components(A), (B) and (C) at the following ratios: Component (A): 10 to 80 mass%; Component (B): 5 to 70 mass %; and Component (C): 5 to 50 mass %. 4.The cover tape according to claim 1, wherein (A) the ionic liquidcontaining a cyclic quaternary nitrogen-containing cation is animidazolium salt.
 5. The cover tape according to claim 1, wherein thecations in (B) the quaternary ammonium salt have one alkyl group oralkenyl group having 10 to 20 carbon atoms.
 6. The cover tape accordingto claim 1, wherein (C) the polyalkylene glycol is a polyethylene glycolhaving a mass-average molecular weight (Mw) of 200 to
 600. 7. The covertape according to claim 1, wherein the thickness of the antistatic layeron the surface on the heat seal side is 0.01 to 0.2 μm.
 8. An electroniccomponent package using the cover tape according to claim 1.